The barrage smashed buildings and sent plumes of black smoke towering over the crowded camp on the Mediterranean.

The fierce, two-day battle has killed nearly 50 combatants and an unknown number of civilians, raising fears that Lebanon’s worst internal violence since the 1975-1990 civil war could spread in a country with an uneasy balancing act among various sects and factions.

Refugees in the Nahr el-Bared camp, on the outskirts of the northern port city of Tripoli, hid in their homes as fighting raged, and Palestinian officials in the camp said nine civilians were killed yesterday. Reports from the camp could not be confirmed because officials and reporters could not get inside.

“There are many wounded. We’re under siege. There is a shortage of bread, medicine and electricity. There are children under the rubble” of damaged buildings, Sana Abu Faraj, a resident of the camp, told al-Jazeera television by cellphone.

The army is seeking to uproot a militant group called Fatah Islam, which arose in the camp late last year. The group touts itself as a Palestinian liberation movement, but many view it as a nascent branch of al Qaeda-style terrorism with ambitions of carrying out attacks around the region.

Nevertheless, the military assault adds yet another layer of instability to Lebanon’s potentially explosive politics. Prime Minister Fuad Saniora’s government already faces a domestic political crisis, with the opposition led by Hezbollah demanding its removal.